feat: add casting module scaffolding (disabled)

Import Chromecast, AirPlay, and DLNA casting scaffolding from separate
branches. The module is currently disabled due to:

- Thread safety issues: rust_cast uses Rc internally (not Send)
- API compatibility: rupnp methods have changed

The scaffolding includes:
- Chromecast: mDNS discovery, device connection, media server
- AirPlay: Discovery scaffolding (RAOP playback pending)
- DLNA/UPnP: SSDP discovery scaffolding (playback pending)

To enable casting in the future:
1. Fix rust_cast thread safety (or use spawn_blocking)
2. Update rupnp API calls for current version
3. Add Deserialize derive to metadata types
4. Uncomment cast module in lib.rs
5. Wire up commands in invoke_handler

package-lock.json

@@ -10,6 +10,7 @@
       "license": "MIT",
       "dependencies": {
         "@tauri-apps/api": "^2",
+        "@tauri-apps/plugin-clipboard-manager": "^2",
         "@tauri-apps/plugin-dialog": "^2.5.0",
         "@tauri-apps/plugin-opener": "^2",
         "lucide-svelte": "^0.562.0",
@@ -1234,6 +1235,15 @@
         "node": ">= 10"
       }
     },
+    "node_modules/@tauri-apps/plugin-clipboard-manager": {
+      "version": "2.3.2",
+      "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-clipboard-manager/-/plugin-clipboard-manager-2.3.2.tgz",
+      "integrity": "sha512-CUlb5Hqi2oZbcZf4VUyUH53XWPPdtpw43EUpCza5HWZJwxEoDowFzNUDt1tRUXA8Uq+XPn17Ysfptip33sG4eQ==",
+      "license": "MIT OR Apache-2.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.8.0"
+      }
+    },
     "node_modules/@tauri-apps/plugin-dialog": {
       "version": "2.5.0",
       "resolved": "https://registry.npmjs.org/@tauri-apps/plugin-dialog/-/plugin-dialog-2.5.0.tgz",